In reply to Louis.

It should be noted that the decision-making structure for WordPress has never been democratic. It is more based on merit with the project lead, the final decision-maker, at the top.

I am willing to take Matt at his word that the feedback and testing show that fullscreen mode is a better experience, but I would rather see the data behind that. I am not a fan of pushing such a change so late in the dev cycle, particularly if it's something that could have waited and become a better experience (e.g., perma-storing the preference via user metadata).

Criticism of ideas and decisions is discussion worth having in the comments. Simply being critical of a person is not and tends to lead the discussion astray.